Abstract
Additive manufacturing (AM) approaches such as Laser Powder Bed Fusion (L-PBF) are being explored to reduce manufacturing costs of gas turbine components. Surfaces of additively manufactured components exhibit distinctive roughness characteristics that significantly affect the pressure losses and heat transfer. For this study, a coupon with a vertical internal flow passage was created using L-PBF and characterized using x-ray tomography. The roughness pattern was extracted using the spanwise-planar extraction approach. Also, two surfaces consisting of distributions of ellipsoids were created to capture the important statistical characteristics of the original rough surface. The resulting roughness geometries were scaled by 102x and applied to the internal wall of the Roughness Internal Flow Tunnel (RIFT). Measurements of friction losses and velocity profiles were obtained. Detailed Reynolds-Averaged Navier Stokes (RANS) simulations using grid-resolved roughness of flow in the RIFT were also performed using an in-house Computational Fluid Dynamics (CFD) code. The present approach combining experimental measurements and CFD simulation of an up-scaled roughness coupon provides a more detailed picture of the flow-field within the roughened channel than was previously available. The measured friction factor of the baseline up-scaled rough channel is within 15% of the original engine-scale channel within the fully turbulent regime. The ellipsoid surfaces are seen to have a friction factor 30% lower than the up-scaled rough channel; the authors hypothesize that this is due to bulk span-wise ridges being present in the up-scaled rough surface but not in the ellipsoid surfaces.
